The Narrator talks about change as Aki has appeared to have bought Fuyuki trunks. Fuyuki tells her he doesn't wear that brand, and she apologizes. She then tells him to try some on, and wear something new.
Keroro notices Fuyuki's discomfort and he decideds to do a new invasion plan; a war between Trunks and Briefs. The other Keroro Platoon members agree, and thus Kururu has one pair of each underwear type come alive.
Fuyuki is then unknowingly thrust into a battle, when at Kissho Academy he notices most other boys wear trunks. Fuyuki appears to have chosen trunks as he places the briefs into his drawers.

The next day Fuyuki notices that all his briefs are missing, as Natusmi informs him she threw them away. Fuyuki appears to have chosen trunks, when Momoka, who was informed of Fuyuki's change in underwear, tells him to never change. Fuyuki is then brought back nostalgia as he recalls all the times he had worn briefs. Fuyuki leaves school, to get the briefs back and after he does he promises to wear the trunks some other time.